The present invention relates to heat seal monitoring devices of a container, which more particularly contains calogenic material making it possible to detect an attempt at a forced entry burglary with respect to the container and/or the material contained therein, or a theft, even in the case where the thief succeeds in refitting the monitoring device.
It more particularly applies to the monitoring of a large number of fixed or mobile container, e.g. 400 to 500 containers, containing radioactive calogenic material, no matter what the thermal environment of said container. In this case, the container containing the calogenic material has parts which, as a result of heat exchanges, have different temperatures to the ambient temperature.
At present, there are a certain number of monitoring devices making it possible to detect the attempted opening of a container. One of these devices involves fixing the ends of a cable passing through the knuckle joint or closing scoops or louvers of a container to a box, in which has been poured a resin material, which has cracked on cooling. These cracks form a clearly defined design, which is photographed at the outset. When somebody attempts to open and then re-seal the box, the resin material contained therein can move and/or new cracks can appear. These changes can be observed by photographing the resin again.
However, detection is not possible in the case where the thief does not touch the box and takes the precaution of only cutting the cable, which is then joined together again by splicing. Moreover, as the monitoring of such a device requires a physical presence, it does not permit a continuous monitoring of the containers. Moreover, in the case of radioactive materials, this device involves an undesirable exposure of the monitoring personnel to the radiation emitted by said materials.
Monitoring devices are also known which permit a continuous or real time monitoring, like those described in EP-A-0018 198. These devices use optical seals, which do not make it possible to make a distinction between calogenic and non-calogenic materials. Moreover, they do not make it possible to detect an intrusion into the container when the seals are left intact.
The present invention relates to burglar-proof monitoring devices for a container, which more particularly contains a calogenic material, making it possible to obviate the aforementioned disadvantages and which make it possible to detect any attempted burglary and/or theft, no matter the location at which this takes place. It is based on the fact that any modification to the container or its content disturbs the thermal state of the container surface to which the sealing device is fixed. Container is understood to mean any sealed enclosure and particularly a member.
The use of heat sensors associated with a data acquisition system is known and in particular is described in the article by H. DUANE ARLOWE, Nuclear Materials Management, 1982, pp. 82 to 88, entitled "A low cost SNM shelf monitor system", relative to the detection of the presence of a container on a shelf and the checking of its calogenic content. However, the latter device permits qualitative rather than quantitative measurements and also does not constitute a sealing device.